The present invention relates to traction control systems and in particular to a traction control system for use on a motor vehicle which system uses a conventional vacuum brake booster and the vehicle's engine manifold vacuum to effect traction control in a vehicle that is not otherwise equipped with an independent source of pressurized braking fluid.
Traction control systems, closely related to anti-lock braking systems, are systems which utilize the vehicle's brakes to absorb a portion of the driving force applied to the driven wheels of the vehicles to obviate slipping of the wheels during acceleration. Typically, these systems utilize wheel speed sensors, brake pressure modulators, an electronic control unit, and the like components of an anti-lock braking system to sense behavior of the vehicle's driven wheels and to generate control signals necessary to prevent wheel spin.
In one type of anti-lock braking system, commonly referred to as a pump-back system, the vehicle's vacuum boosted master cylinder is utilized as a source of pressurized braking fluid during anti-lock braking system operation. A small pump is used to replenish brake fluid lost from the system during brake pressure decay cycles. This type of system is not readily adaptable to traction control because the vehicle's brakes are not used during acceleration, and accordingly, no source of pressurized brake fluid is available to operate the vehicle brakes. Traction control systems which work in conjunction with a pump-back anti-lock braking system have been proposed, but such systems typically require the addition of a full-time hydraulic pump, additional brake pressure modulating valves and similar components. This produces a system which, is effective but also expensive and complex. There therefore exists a need for a traction control system which is particularly well adapted for use in conjunction with pump-back anti-lock braking systems and in particular to such a system that does not require the addition of a significant number of components.
Broadly, the present invention is a traction control system wherein an electronically controlled solenoid valve and related pneumatic circuitry apply the variable vacuum of a motor vehicle's intake manifold to that side of the diaphragm of the vehicle's vacuum booster normally exposed to atmospheric pressure during braking to provide initial actuation of the master cylinder during traction control conditions. The pressurized braking fluid generated by the master cylinder is selectively applied to only the driven wheels of the vehicle during traction control. Because the intake manifold vacuum varies indirectly in proportion to engine power during acceleration, application of this vacuum provides a variable pressure source of braking fluid in which the available traction absorbing braking torques vary in direct proportion to the torques required during acceleration thereby obviating jerky, uneven, or excessive traction control torque on the vehicle's wheels.
In a specific embodiment of the invention, the system includes a master cylinder having a vacuum booster. At least one brake wheel cylinder associated with a driven wheel of a motor vehicle is operatively connected to the master cylinder. Means are provided responsive to the rotational behavior of the vehicle's wheels for generating traction control signals. Pneumatic switching means are provided for connecting the side of the vacuum booster diaphragm normally exposed to atmospheric pressure to the vehicle's manifold vacuum. Brake pressure modulating means are connected to the traction control signal generating means for modulating the application of pressurized braking fluid from the master cylinder to the wheel brake cylinders of the vehicle's driven wheels.
It is therefore an object of the invention to provide an improved traction control system.
Another object of the invention is to provide such a system adaptable for use with pump-back anti-lock braking systems.
Still another object of the invention is to provide a traction control system in which the variable of vacuum engine manifold pressure is utilized as a variable vacuum source for the vacuum booster of the vehicle's braking system during traction control operation.
Another object of the invention is to provide a traction control system in which traction absorbing torque provided by the vehicle's braking system varies in direct proportion to available power for acceleration.
Yet another object of the invention is to provide a traction control system operable in conjunction with a pump-back anti-lock braking system using an existing pump and brake pressure modulator means.
Still another object of the invention is to provide such a system which is substantially fail-safe, simple, and economical to produce.